American retailers have never been shy about extending their operating hours during the weeks between Thanksgiving and Christmas, when most of their profits are made. But last-minute holiday shopping just got more extreme: Macy's, the nation's second-largest department store chain, on Friday announced that it will keep doors open at most locations for 48 hours straight during the weekend before Christmas.

The retailer's now-misnamed "One Day Sale" will last from 7 a.m. on Dec. 21 until 7 a.m. on Dec. 23. At that point, the sale will end, but Macy's will remain open for the remainder of the day.

Don't expect the round-the-clock shop-a-thon to go unnoticed. "If it works well for Macy's, I can guarantee it will be a trend next year," says Dan Butler, vice president of merchandising and retail at the National Retail Federation.

Macy's tradition of staying open for 24 hours shortly before Christmas to lure last-minute holiday shoppers began in 2006 at the Macy's Queens Center in New York, and subsequently spread to other locations.

Staying open for two days straight is a first, however.

Butler points out that the extended pre-Christmas shopping marathon comes in the wake of a successful extended Black Friday, during which some retailers opened their doors Thanksgiving Day for the first time. "I think a lot of people were surprised by the big rush to shop," he says.

"Not all shoppers want to shop at crazy hours, but some do, and the stores are accommodating them," continues Butler. "There are a lot of people who work the third shift, or second shift, and for them it's not convenient to come in during the day."

As for Macy's, staying open isn't necessarily an inconvenience. "A lot of stores have people there doing restocking at night," says Butler, "so I think Macy's just thought, if we have staff there, why not just open for business?"